Linear motion variable resistor with carbon and spring metal contacts

ABSTRACT

A slide is movable lengthwise between spaced parallel collector and resistance strips. A carbon contact between the strips engages the resistance strip, and a sheet metal spring contact compressed between the carbon contact and the collector strip is connected to the carbon contact. Either of the contacts is connected with the slide for movement lengthwise of the strips. The spring has legs extending in opposite directions along the collector strip in sliding engagement with it and presses the carbon contact against the resistance strip.

- United States Patent [72] inventor Mogelll W. Bang 3,363,212 1/1968 Joy 338/202 X RidgwayJa. 3,504,326 3/1970 Campbeil.... 338/183 [21] Appl. No. 92,706 3,582,860 6/1971 Milovac 338/202 X 2: :"f d 32: Primary Examiner-Lewis H. Myers e St C rho C Assistant Examiner-Gerald P. Tolin Po H Attorney-Brown, Murray, Flick & Peckham St.. Marys, Pa. 7

ABSTRACT: A slide is movable lengthwise between spaced [54] LINEAR MOTION vARIABLE RESISTOR WITH parallel collector and resistance strips. A carbon contact CARBON AND SPRING METAL CONTACTS between the strips engages the resistance strip, and a sheet 8 Claims, 8 Drawing Figs.

- metal spring contact compressed between the carbon contact [52] U.S.Cl 338/183, and the collector strip is connected to the carbon contact.

- 3 8/202 Either of the contacts is connectedwith the slide for move- [51] int. Cl. l-l0lc 9/02 ment lengthwise of the strips. The spring has legs extending in [50] Field of Search 338/ 1 18, opposite directions along the collector'strip in sliding engage- 160, 176, 183, 202 ment with it and presses the carbon contact against the ret [56 1 References Cited mp UNITED STATES PATENTS 3,096,500 7/1963 Daily 338/183 a M 4 5y /6 3 -t ;7 6 I -I /0 L v j LINEAR MOTION VARIABLE RESISTOR WITH CARBON AND SPRING METAL CONTACTS It is among the objects of this invention to provide a linear motion variable resistor, in which a metal spring constantly presses a carbon contact against a resistance element, and in which the spring slides along a collector element and electrically connects the collector and carbon contact.

The invention is illustrated in the accompanying drawings, in which FIG. 1 is a side view, partly broken away, of a linear motion potentiometer;

FIG. 2 is an enlarged fragmentary longitudinal section taken on the line II--II of FIG. 1;

FIG. 3 is an enlarged cross section taken on the line IIIIII of FIG. 2;

FIG. 4 is a fragmentary side view of a slide with its bridging contacts, showing a modification;

FIG. 5 is a longitudinal section taken on the line V-V of FIG. 4;

FIG. 6 is a view, similar to FIG. 5, of another modification;

FIG. 7 is a fragmentary side view of a further embodiment of the invention; and

FIG. 8 is a longitudinal section taken on the line VIII-VIII of FIG. 7.

Referring to FIGS. 1 to 3 of the drawings, the long rectangular case 1 of a variable resistor, such as a potentiometer, is provided along its front or top with a central slot 2 extending lengthwise of the case for nearly its full length. Slidably mounted in the slot for movement lengthwise of the case is a rectangular slide 3 that has laterally opening grooves 4 in its opposite sides receiving the sidewalls of the housing slot to hold and guide the slide. The slide may be moved in any suitable manner, such as by a projection or knob 5.

Inside the case a metal collector strip 6 and an electrical resistance strip 7 are mounted against its opposite sides in parallel relation to each other. The collector strip is provided with an integral terminal 8 that extends through the back or bottom of the case, and each end of the resistance strip is connected to another terminal 9 likewise extending through the back. The slide 3 has a portion extending between these two strips, from which it is spaced. This portion of the slide is an open frame 10 that is parallel, or nearly so, to the collector and resistance strips. The frame preferably is rectangular.

Disposed in the opening through the frame, but projecting from it, is a carbon show orbloek 11. Carbon as used herein is intended to cover graphite also. The block is rectangular to fit in the frame, which is provided inside with short ribs 12 slidingly engaged by the block to reduce friction between it and the frame. The block engages the resistance strip 7, with which it makes substantially a line contact, due to the taper of the projecting side of the block The contact block is pressed against the resistance strip and also electrically connected with the collector strip by means of a sheet metal spring member compressed between the block and the collector. To connect the spring tightly to the block, the spring is formed from a narrow metal strip 13 provided with a central laterally projecting U-shaped portion formed by bending the strip on itself as shown in FIG. 2. This bent portion projects into a central opening 14 in the contact shoe and tightly engages opposite sidewalls of that opening. Struck out tongues 15 dig into the sidewalls of the opening to help hold the spring in place. The parts of the spring strip outside of the block diverge disposed between the resistance strip and the adjacent side of the plate and spaced from both. This central area is provided with parallel side flanges 25 that fit snugly in the upper and lower ends of slots 23. Integral with the central portions of the side flanges are spring legs 26 that are bent to extend lengthwise of the collector strip. Only their ends engage that strip.

Contact with the resistance strip is made by a flat carbon shoe or button 28 provided with a central stem 29 that projects through a central hole in the flat area 24 of the spring. The marginal area of the hole is provided with laterally spaced teeth 30 that are bent inwardly toward the slide when the buttoward the collector strip and have rounded ends 16 pressing against it. The spring therefore makes good electrical contact with the collector and causes the contact block to make good electrical contact with the resistance strip. When the slide is moved along the case, it moves the block and spring with it to vary the electrical resistance. As the block wears, the spring will continue to hold it firmly against the resistance strip.

In the modification shown in FIGS. 4 and 5, the portion of the slide 20 between the resistance and collector strips 21 and 22 in the case is not a frame, but more of a plate provided with a pair of slots 23 extending upwardly from its bottom. A sheet metal spring member has a relatively large flat central area 24 ton stem is pushed into the hole. The teeth dig into the stem and hold the button firmly against the spring. When the slide is moved lengthwise of the case it moves the spring, which in turn slides the contact button along the resistance strip 21. v

The embodiment of the invention shown in FIG. 6 is similar to the one just described, except that the spring legs 35 are considerably longer and there are a total of three legs. Two

' legs at one side of the flat central area 36 of the spring straddle the one leg at the other side, because the legs cross each other between the slide 37 and the collector strip 38. The contact shoe may be a button as before, or a rectangular block 39 with a tapered side to form a line contact between it and the resistance strip 40. i

A still further modification is shown in FIGS. 7 and 8. Here again the slide has a frame portion 42 between the resistance and collector strips 43 and 44, but the contact shoe 45 does not fit in the frame. It is provided with a central stem 46 plugged into a hole in the central area 47 of a sheet metal spring, as in FIGS. 4 to 6. At the sides of the upper and lower comers of the spring there are lateral extensions 48 that extend around the sides of the frame and clamped onto it to hold the spring in place. At the opposite sides of the spring there are integral legs that cross each other between the slide and the collector strip, against which their ends press. Preferably, there is one leg 49 at one side of the spring, straddled by two legs 50 at the opposite side.

With the construction disclosed herein, the best materials are provided for engagement with the two strips. Thus, a carbon contact slides along the resistance strip, but a metal contact slides along the collector. The two sliding contacts are firmly secured together, and the spring assures good contact with the strips even though the carbon contact may wear. Another advantage is that the contact assembly has three points of contact with the strips; one with the resistance strip and two with the collector strip. This three-point support for the contacts provides for a stable chatter-free movement of the contact assembly as compared with the usual two point contact support design.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and .described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Iclaim:

l. A variable resistor comprising spaced parallel collector and resistance strips, a slide between said strips movable lengthwise thereof, a carbon contact member between the strips and engaging the resistance strip beside the slide, and a sheet metal spring member compressed between said contact member and the collector strip and having a central portion connected to the contact member, one of said members being connected with the slide for movement by it lengthwise of the strips, said spring member having legs extending in opposite directions along the collector strip in sliding engagement with it and pressing said contact member against the resistance strip.

2. A variable resistor according to claim 1, in which said slide includes a, frame spaced from said strips and containing said contact member, said contact member is a carbon block projecting from the frame and provided with a central opening in the side nearest the collector strip, and said central portion of the spring member is bent to fit in said block opening.

3. A variable resistor according to claim 1, in which said central portion of the spring member is provided with integral clamp portions clamped onto said slide.

4. A variable resistor according to claim 3, in which said legs cross each other.

5. A variable resistor according to claim 3, in which said central portion of the spring member is provided with a central opening, and said contact member is a carbon show provided with a stern mounted in said opening.

6. A variable resistor according to claim 1, in which said 'central portion of the spring member is provided with a central opening, and said contact member is a carbon shoe provided with a stem mounted in said opening. 

1. A variable resistor comprising spaced parallel collector and resistance strips, a slide between said strips movable lengthwise thereof, a carbon contact member between the strips and engaging the resistance strip beside the slide, and a sheet metal spring member compressed between said contact member and the collector strip and having a central portion connected to the contact member, one of said members being connected with the slide for movement by it lengthwise of the strips, said spring member having legs extending in opposite directions along the collector strip in sliding engagement with it and pressing said contact member against the resistance strip.
 2. A variable resistor according to claim 1, in which said slide includes a frame spaced from said strips and containing said contact member, said contact member is a carbon block projecting from the frame and provided with a central opening in the side nearest the collector strip, and said central portion of the spring member is bent to fit in said block opening.
 3. A variable resistor according to claim 1, in which said central portion of the spring member is provided with integral clamp portions clamped onto said slide.
 4. A variable resistor according to claim 3, in which said legs cross each other.
 5. A variable resistor according to claim 3, in which said central portion of the spring member is provided with a central opening, and said contact member is a carbon show provided with a stem mounted in said opening.
 6. A variable resistor according to claim 1, in which said slide is provided between said strips with a pair of parallel slots therethrough spaced lengthwise of the strips, and said spring member has intermediate parallel portions connecting said central portion to said legs, said parallel portions being slidably mounted in said slots.
 7. A variable resistor according to claim 6, in which said legs extend across each other.
 8. A variable resistor according to claim 6, in which said central portion of the spring member is provided with a central opening, and said contact member is a carbon shoe provided with a stem mounted in said opening. 